/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *      http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.catalina.util;

/**
 * Encode an MD5 digest into a String.
 * <p>
 * The 128 bit MD5 hash is converted into a 32 character long String. Each
 * character of the String is the hexadecimal representation of 4 bits of the
 * digest.
 * 
 * @author Remy Maucherat
 * @version $Revision: 467222 $ $Date: 2006-10-24 11:17:11 +0800 (星期二, 24 十月
 *          2006) $
 */

public final class MD5Encoder {

	// ----------------------------------------------------- Instance Variables

	private static final char[] hexadecimal = { '0', '1', '2', '3', '4', '5',
			'6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f' };

	// --------------------------------------------------------- Public Methods

	/**
	 * Encodes the 128 bit (16 bytes) MD5 into a 32 character String.
	 * 
	 * @param binaryData
	 *            Array containing the digest
	 * @return Encoded MD5, or null if encoding failed
	 */
	public String encode(byte[] binaryData) {

		if (binaryData.length != 16)
			return null;

		char[] buffer = new char[32];

		for (int i = 0; i < 16; i++) {
			int low = (int) (binaryData[i] & 0x0f);
			int high = (int) ((binaryData[i] & 0xf0) >> 4);
			buffer[i * 2] = hexadecimal[high];
			buffer[i * 2 + 1] = hexadecimal[low];
		}

		return new String(buffer);

	}

}
